Les Verts (the Greens) and the Europe Ecologie (EE) parties meet Saturday in Lyon for a congress to approve the merger and agree on a new name for the future party.
Les Verts were established in 1984 in a fusion of an environmentalist party and various groups, and in 1997 they gained seven seats in the national parliament.
The EE’s most prominent member is European member of parliament Daniel Cohn-Bendit.
Last year, the two parties joined forces in the European Parliament elections, gaining 16.3 per cent of the French vote. Their success continued in regional elections early in 2010.
On August 21, the two parties also agreed to nominate former investigative judge Eva Joly as their joint candidate for the 2012 French presidential elections.